1. Field of the Invention
The present invention relates to a driving method and a driving device for a standing-wave-type ultrasonic actuator.
This application is based on Japanese Patent Application No. 2007-000770, the content of which is incorporated herein by reference.
2. Description of Related Art
Recently, ultrasonic motors have been drawing attention as a new type of motor replacing electromagnetic motors. Ultrasonic motors have the following advantages over known electromagnetic motors:    1) Ultrasonic motors are capable of high torque without using gears;    2) Ultrasonic motors have holding force when powered off;    3) Ultrasonic motors have high resolution;    4) Ultrasonic motors are quiet; and    5) Ultrasonic motors do not generate magnetic noise and are unaffected by noise.
Ultrasonic motors are classified into traveling-wave-type ultrasonic motors and standing-wave-type ultrasonic motors based on the principle of wave propagation. As one example of an ultrasonic motor in the related art, Japanese Unexamined Patent Application, Publication No. 2002-199749 discloses a traveling-wave-type ultrasonic motor. In Japanese Unexamined Patent Application, Publication No. 2002-199749, sound generation is reduced when activating and when stopping the device by gradually changing a phase difference between AC driving voltages when going from a standing wave to a traveling wave during activation of the ultrasonic motor, and when going from a traveling wave to a standing wave when stopping the ultrasonic motor.